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>3.2. Important parts of the kernel</A
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>The Linux kernel consists of several important parts: process
	management, memory management, hardware device drivers, filesystem
	drivers, network management, and various other bits and pieces.
	<A
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>Figure 3-1</A
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	shows some of them.</P
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>Figure 3-1. Some of the more important parts of the Linux kernel</B
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>Probably the most important parts of the kernel (nothing else
	works without them) are memory management and 
	process management.  Memory management takes care of assigning
	memory areas and swap space areas to processes, parts of the
	kernel, and for the buffer cache.  Process management creates
	processes, and implements multitasking by switching the
	active process on the processor.</P
><P
>At the lowest level, the kernel contains a hardware device
	driver for each kind of hardware it supports.  Since the world is
	full of different kinds of hardware, the number of hardware device
	drivers is large.  There are often many otherwise similar pieces
	of hardware that differ in how they are controlled by software.
	The similarities make it possible to have general classes of
	drivers that support similar operations; each member of the class
	has the same interface to the rest of the kernel but differs in
	what it needs to do to implement them.	For example, all disk
	drivers look alike to the rest of the kernel, i.e., they all
	have operations like `initialise the drive', `read sector N',
	and `write sector N'.</P
><P
>Some software services provided by the kernel itself have
	similar properties, and can therefore be abstracted into classes.
	For example, the various network protocols have been abstracted
	into one programming interface, the BSD socket library.  Another
	example is the <I
CLASS="GLOSSTERM"
>virtual filesystem</I
> (VFS)
	layer that abstracts the filesystem operations away from their
	implementation.  Each filesystem type provides an implementation
	of each filesystem operation.  When some entity tries to use
	a filesystem, the request goes via the VFS, which routes the
	request to the proper filesystem driver.</P
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